Mitomycin C (MMC) is a clinically active antineoplastic agent used against a wide variety of solid tumors. Studies on the drug's mechanism of action have primarily focused on: identifying the enzymes responsible for its activation; its interaction with nuclear DNA; and its ability to generate oxygen radicals. While several studies have been done in these areas as well as others, its mechanism of action is still not completely understood. We have recently identified xanthine dehydrogenase (XDH) as an enzyme capable of bioactivating mitomycin c to form reactive metabolites. This was the first report of xanthine dehydrogenase's role as an enzyme involved in the: bioactivation of an anticancer agent. The studies in this proposal are designed to study xanthine dehydrogenase's role in tumor cells in terms of its involvement in the bioactivation of chemotherapeutic agents and the potential efficacy of targeting agents against this enzyme. Studies are also designed to more specifically study the interaction of MMC with this enzyme and further probe MMC's cytotoxic mechanism of action. The main thrusts of this proposal are the following: studies are planned to compare the kinetics of the enzymatic activation of mitomycin c by (XDH) isolated from human (MCF-7) and mouse (EMT6) breast tumor tissues; studies are designed to determine the role of (XDH) in MMC bioactivation in these same breast tumor lines under different physiological conditions (aerobic vs hypoxic and at different pHs); studies are planned with CHO mutant cell lines to probe the type and relative toxicities of DNA lesions induced by (XDH) activated MMC and to determine whether the differences in these different cell line's sensitivity to MMC can be correlated to (XDH) levels; studies are designed to determine whether (XDH) can activate other bioreductive anticancer agents such as the anthracyclines and [Tirapazamine (SR 4233)] and finally studies, are planned to determine the activity of (XDH) in a variety of human tumor cell lines and compare these to activities found in normal human tissues. These proposed studies will provide important data which will help elucidate MMC's mechanism of action and xanthine dehydrogenase's role in the bioactivation of other clinically relevant anticancer agents.